1. Field of the Invention
The present invention relates to a magnetic sensor for detecting change in magnetic flux crossing a magnet-sensing plane caused by a rotating magnet, and more particularly to a magnetic sensor detecting a greater rotational angle of the magnet to be and facilitating mass-production.
2. Related Art
The applicant has proposed a magnetic sensor disclosed in the coassigned U.S. patent application filed on Jun. 3, 1992 under Ser. No. 07/893,002 now U.S. Pat. No. 5,278,497 as shown in FIGS. 1 and 2. Specifically, FIG. 1 is a cross-sectional view showing the proposed magnetic sensor and FIG. 2 is a schematic view showing the relationship between a magnet and a ferromagnetic resistive element (hereinafter merely referred as MR element.
The proposed magnetic sensor of Ser. No. 07/893,002 now U.S. Pat. No. 5,278,497 as shown in FIG. 1 is provided with a resin frame 1, a rotating shaft 2 mounted rotatably in the frame 1, an arm 3 fixed to one end of the rotating shaft 2, a cylindrically molded case 4 formed on the other end of the rotating shaft 2, and a magnet 6 accommodated into and secured to the molded case 4 by an adhesion 7.
The magnetic sensor is further provided with a ceramic substrate 8 on which an MR element 9 is mounted. The substrate 8 is a circuit substrate on which a pattern of electric wiring is formed and various kinds of electronic devices are mounted, now shown. The ceramic substrate 8 is mounted on the frame 1 with an outer diameter of the substrate. As shown in FIG. 2, the MR element 9 is provided with a rectangular-shaped magnet-sensitive plane 9a consisting by molding of comb-like patterns 10a, 10b formed of a ferromagnetic resistive material and arranged to cross each other, a ground (GND) terminal 11a, a Vcc terminal 11b and an output terminal 11c, so that the magnet-sensitive plane 9a directs perpendicular to the magnet 6. The magnetic sensor also has an input/output terminal 12.
The operation of the proposed magnetic sensor will now be described hereinbelow.
When the arm 3 rotates in association with the opening/closing condition of a throttle valve (not shown) disposed in an intake conduit performing as an air-flow path of a vehicle, for example, the rotation of the arm 3 is transmitted to the magnet 6 through the rotating shaft 2, that is, the magnet 6 rotates in association with the arm 3.
By the rotation of the magnet 6, the magnetic flux, generated from the magnet 6 and crossing the magnet-sensitive plane 9a, varies and, as a result, the resistance value of the magnetic resistive pattern of the MR element 9 varies in accordance with the variation of the magnetic flux crossing the magnet-sensitive plane 9a. The MR element 9 outputs a voltage corresponding to the rotational angle of the magnet 6.
The output voltage of the MR element 9 is amplified and then output through the input/output terminal 12 to the outside devices (not shown), and the opening/closing condition of the throttle valve is thus detected.
The detection by the MR element 9 will be described in more detail with reference to FIG. 2.
A predetermined voltage is applied between the GND terminal 11a and the Vcc terminal 11b, and the output terminal 11c outputs a voltage obtained by the resistance division of the comb-like patterns 10a and 10b.
When the magnet 6 rotates along an arrow D shown in FIG. 2, the magnetic flux crossing the comb-like patterns 10a and 10b varies accordingly, and the resistance values of the comb-like patterns 10a and 10b also vary and, as a result, the output voltage from the output terminal 11c changes. The output voltage from the output terminal 11c has a sine wave corresponding to the rotation of the magnet 6 as indicated by a line A shown in FIG. 3. As shown in FIG. 3, the output voltage of the output terminal 11c and the rotational angle of the magnet 6 have a linear correlation within a range of angle .+-.35.degree.. Accordingly, the previously proposed magnetic sensor is capable of detecting the rotational angle of the magnet 6 within the range .+-.35.degree..
Since the magnet-sensitive plane 9a of the MR element 9 according to the proposed magnetic sensor is constituted by the comb-like patterns 10a and 10b crossing each other, the rotational angle of the magnet 6 which can be detected is limited to be small.